Effect of altitudinal gradients on forest structure and composition on ridge tops in Garhwal Himalaya

Abstract

Ridge top ecosystems (RTEs) are considered to be more sensitive to global warming as they are characterized by uniform sunlight exposure and low human interferences and hence are perfect places for monitoring and comparing the effects of climate change in species composition. The present study was carried out on RTEs of four different mountain ranges, viz. (1) Narendranagar–Hindolakhal (2) Mussoorie–Dhanolti (3) Chaurangikhal–Harunta and (4) Dayara–Gidara, along altitudinal gradient (situated below 2000 to above 3500 m), in Garhwal Himalaya to understand the variation in tree composition and distribution range. 0.1 ha-sized sample plot was used to analyze the tree species, whereas 5 m × 5 m for saplings and 1 m × 1 m for seedlings. The tree layers on RTEs were consisted of total 69 tree species, belonging to 55 genera and 39 families. Shorea robusta, Pinus roxburghii, Rhododendron arboreum, Quercus leucotrichophora, Q. floribunda, Q. semecarpifolia, Cedrus deodara, Pinus wallichiana and Abies spectabilis were found as the dominant and well-occupied tree species on the RTEs from lower to higher elevations. The mean stand density was recorded as 597 ± 29 trees ha−1 (ranged between 546 and 616 trees ha−1) with a mean basal cover of 77.25 ± 17.90 m2 ha−1 (ranged between 54.43 and 102.83 m2 ha−1). A traditional pattern for tree diversity was recorded which decreased with increasing altitude. The detrended correspondence analysis ordination plot clumped the species together which shared the same habitat and environmental conditions which revealed that elevation and geographic location were the dominant factors for regional differences in species composition among RTEs.